Conditions of Clarity Grading

The basis of a reliable and universally acceptable
quality determination are clearly defined and universally applicable
descriptions and especially definitions of descriptions for the typical
type of inclusion in every clarity grade. A limiting factor is that
because of the nearly limitless number of types of inclusions it is not
possible to form an absolute definition. In the practice of clarity
grading there will always be border-line cases which require a certain
tolerance, even if the grading is done by experts.

The classification of internal defects in a clarity
grade depends on many factors, which have to be considered and which
only lead to a reliable determination if all aspects are taken into
account. No two diamonds are alike, yet every grade of clarity comprises
characteristic and specific features.

When examining the inclusions, it is most important to
observe them through the crown:

size and number of inclusions

discernibility of inclusions

whether they can be seen with or without
difficulty, with magnification or with the naked eye

appearance of inclusions

whether light, colorless or dark and colored

nature of inclusions

whether unalterable crystalline
inclusions or risky cracks which could expand in the stone under
pressure or a blow

position of inclusions

whether under the table or around the
girdle

type of inclusion

whether compact or diffuse, dot-like or
flat

influence on brilliance and durability of
stone.

Measuring instruments which can register the size and
number of inclusions, cannot take into account the other very important
factors. Only the human eye can do that, therefore the author disagrees
with the use of scanning microscopes for the "measurement" of inclusions
for clarity grading.

An individual inclusion in a cut diamond can appear
more definite than a collection of several smaller Inclusions and a
colorless transparent mineral inclusion is less obvious than a colored
inclusion of the same size. colored inclusions influence the brilliant
effect more strongly and can easier be seen with the naked eye, while
colorless inclusions up to a certain clarity grade can only be
recognized with a 10 x magnification.

The position of the inclusions in a stone is also of
importance. It is more easily discern able in the centre or Just under
the table of a stone than under the pavilion facets or near the girdle.
In the latter case it is more "hidden" by the edges of the facets and by
the reflection of single facets because of the larger contrast between
light and dark.

This may lead to the differential grading of two
similar inclusions in different positions (Fig 44 and 45).

Fig 44 A cloud under the table - VS 1

Fig, 45 The cloud in Fig 45. positioned near
to the girdle. VVS 2

Inclusions near the facet edge are often reflected in
several facets (Fig 46 and 47), they are therefore more easily visible
and their grading is lower than similar inclusions which are not
reflected.

Fig 46 A light inclusion with two
reflections

Fig 47 A crystal inclusion in the centre
with several reflections in the pavilion (30x)

Fracture-, cleavage- and tension-cracks can be
enlarged and expanded by external mechanical stress (for instance during
the setting or while removing a stone from its setting, exposure to
blows or even taps, sudden temperature chances) and detract from the
durability of the stone. Therefore larger cracks are generally evaluated
somewhat lower than solid crystalline inclusions which cannot change any
further.

Cracks which have an edge orientated in the viewing
direction are evaluated higher than those perpendicular to the crack
plane appearing flat and as a plane (Fig 48 a and b).

Fig 48b The cleavage crack of Fig 45a with
the edge of the crack perpendicular to the viewing -direction =
SI

Cracks which reach the surface of the stone contain
sometimes a colored liquid which makes them more obvious and diminishes
the brilliance.

Grades of clarity, similar to grades of color, form
step-less transitions to the following grade with increasing size and
number. It is difficult to clearly' define such quality steps', apart
from the already mentioned conditions the following factors must be
considered:

magnification used

condition of light

visual faculty

the grader.

As basis for clarity grading the 10 x magnification
with an achromatic and aplanatic loupe is internationally accepted. This
can refer to a hand loupe or a binocular lens of a microscope. The
advantages and disadvantages of the two systems will be discussed later.
The use of a loupe requires the normal or by glasses corrected sight of
the grader.

The grading should be done by an expert in normal
light conditions. The grader should not be a beginner, need not be a
"expert", but should have some experience in diamond grading.

The light which should be used for the determination
of the inclusions should be a white, diffuse light. The day-light lamp
used for color-grading is a suitable instrument. A spot-light should
not be used, because it causes strong surface reflections which make
viewing of the interior of the stone more difficult. The commercial
diamond microscopes have a built-in dark-field illumination, which
illuminates from below through the pavilion facets. This advantageous
illumination can also be made use of with a day-light lamp if the stone
is held immediately in front of the lamp so that the light illuminates
the stone from behind.